Currently, in AU version, system didn't keep user from specifying the 'appl from item entry' field with other item ledger entries or empty. This actually make Business Central more suitable for some special business scenario, but this will also cause some other problems. We have created a sales order, partially shipped and invoiced. After that, we created 'sales credit memo' on the posted sales invoice and kept the 'appl from item entry' field empty. System didn't give us an error message, and the sales credit memo has posted. But when we back to the original sales order, the qty field has not received any modifications or corrections.